Evidence for trichromacy in the green peach aphid, Myzus persicae ...

Journal of Insect Physiology 51 (2005) 1255–1260
Evidence for trichromacy in the green peach aphid, Myzus persicae
(Sulz.) (Hemiptera: Aphididae)
Abstract
S.M. Kirchner ,T.F. Do¨ ring,H. Saucke
Department of Ecological Plant Protection, University of Kassel, Nordbahnhofstr. 1a, 37213 Witzenhausen, Germany
Received 5 May 2005; accepted 6 July 2005
The green peach aphid, Myzus persicae (Hemiptera: Aphididae) is an important phytophagous pest of greenhouse and field crops.
In the host finding process visual cues are of paramount importance. In order to contribute to the understanding of the perception of
visual stimuli in this species,we measured the electroretinogram of alate female summer migrants of M. persicae. The spectral
sensitivity was measured in 10 nm steps under both dark and light adaptation from 320 to 640 nm. The dark adapted spectral
sensitivity curve showed one maximum in the green region around 530 nm and a distinct shoulder between 500 and 510 nm. In
presence of adapting light,a secondary blue–green peak (490 nm) and a third peak in the near UV (330–340 nm) were observed.
From these results we conclude that M. persicae has three spectral types of photoreceptors.
r 2005 Elsevier Ltd. All rights reserved.
Keywords: Aphids; Electroretinogram; Insect vision; Spectral sensitivity
1. Introduction
Myzus persicae is a serious phytophagous pest of
greenhouse and field crops (Miles,1989),acting
indirectly as a vector of many virus diseases (Ossiannilsson,1966;
Sylvester,1989; Radcliffe and Ragsdale,
2002),as well as directly by feeding on plant assimilates
(Hoffmann and Schmutterer,1999).
In the host finding process visual cues are of major
importance (Moericke,1955; Dixon,1985; Klingauf,
1987; but see Chapman et al.,1981; Powell et al.,1995).
There are numerous studies which substantiate the
attractiveness of yellow targets to aphids during alighting
flight (e.g., Moericke,1951; Kring,1967; Gonza´ lez
and Rawlins,1968; Do¨ ring et al.,2004). The preference
of many phytophagous insects species for yellow over
green (Bernays and Chapman,1994) has been inter-
Corresponding author. Tel.: +49 55 42 98 15 69;
fax: +49 55 42 98 15 64.
E-mail address: skirch@uni-kassel.de (S.M. Kirchner).
0022-1910/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jinsphys.2005.07.002
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preted as a super-normal foliage-type stimulus,where
yellow reflects light with a greater intensity in the insectvisible
wavelength range than green (Prokopy and
Owens,1983). Also,the repellence of metallised or
plastic mulches (Smith et al.,1964; Heathcote,1968;
Loebenstein et al.,1975) has been attributed to their
shortwave light-reflecting properties (Kring,1964; Gibson
and Rice,1989),although the key wavelengths are
still unknown (Do¨ ring et al.,2004). For a more
comprehensive understanding of the behavioural reaction
of animals to colours it is necessary to gain
information about the physiological basis of the vision
systems involved (Prokopy and Owens,1983),namely
the spectral sensitivity function. While for flowervisiting
insects like adult Hymenoptera and Lepidoptera,the
electrophysiological spectral sensitivity functions
of many species are known,phytophagous life
stages of insects are surprisingly underrepresented
(Briscoe and Chittka,2001). Until now,only the
cabbage root fly, Delia radicum (L.) (Brown and
Anderson,1996),the western flower thrips,Frankliniella

1256
occidentalis (Pergande) (Matteson et al.,1992),and—as
the only phytophagous Homopteran species—the glasshouse
whitefly, Trialeurodes vaporariorum (Westwood)
(Mellor et al.,1997) have been examined. Especially,
there is no data regarding the spectral sensitivity of
aphids yet (Prokopy and Owens,1983; Gao et al.,2000;
Kelber et al.,2003). Therefore,the aim of this study was
to apply the electroretinogram (ERG) technique (Goldsmith
and Bernard,1974; Brown and Anderson,1996;
Scharstein and Stommel,1999) toM. persicae in order
to contribute to a better understanding of the spectral
properties of the eye and host finding of this agriculturally
most important aphid species.
2. Materials and methods
2.1. Electroretinogram recordings
A 100 W xenon arc lamp (Osram XBO100W/2 OFR)
was used as a light source in Xe-100 lamp housing device
(UV-Gro¨ bel,Ettlingen,Germany). Narrow bandpass
filters (10 nm half-width,from Ealing Davin Optronics,
Watford,UK) provided nearly monochromatic light in
the wavelength range 320–640 nm in 10 nm steps.
Neutral density filters (Ealing) allowed the intensity of
light passing through the bandpass filters to be varied
over approx. 2.5 log units. A manual shutter (T70
camera,Canon) produced 0.5 s light flashes as test
stimuli,which were transmitted through a 3 mm dia.
liquid light guide (UV-Gro¨ bel) into a light-proof Faraday
cage. The terminal end of the light quide was fixed
to a micromanipulator (Prior,Cambridge,UK) at about
1.5 cm distance to the aphid’s eye.
Summer migrants (winged virginoparae) were reared
on chili pepper plants (Capsicum annuum L.) under
crowded conditions in long days (16 h light,8 h dark at
20 and 16 1C,respectively) in an Environmental
Incubator (Inculight 400,Schu¨ tt,Go¨ ttingen,Germany).
The aphids were mounted on double-sided sticky tape
on a 10 10 mm platform. Under a stereomicroscope
(80 magnification,Leica S6E from Leica,Wetzlar,
Germany),legs,wings and antennae were gently secured
on the tape in order to immobilise the aphid. The
recording and indifferent electrodes were made from
electrolytically sharpened 0.2 mm diameter tungsten
wire (Goodfellow,Cambridge,UK). The recording
electrode was inserted into the left eye through the
cornea and the grounded reference electrode was placed
in the abdomen. Light stimuli were applied to the eye
and the response was displayed on a Digital Storage
Oscilloscope (HM205-3 from Hameg,Mainhausen,
Germany) via an AC amplifier equipped with low-pass
(300 Hz) filters and high-pass (0.1 Hz) filters (P-55 from
Grass Telefactor,West Warwick,USA). All recordings
took place at 20 1C.
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2.2. Experimental protocol
The optical system was calibrated at the position of
the aphid’s compound eye by measuring the emitted
light for all possible combinations of our neutral density
filters and bandpass filters with a spectrometer
(RAMSES ACC,from TriOs,Osnabru¨ ck,Germany)
in mW s 1 m 2 . These data were transformed to photon
flux equivalents by multiplication with the respective
wavelengths.
Pretests at 350,450,and 550 nm showed that
intensity–response curves followed log-linear functions.
An appropriate criterion response was selected to ensure
that over the whole wavelength range a constant
response could be produced by adjusting the light
intensity. For each wavelength,0.5 s flashes of 3–5
different light intensities were given to produce responses
near the selected criterion response. The photon
flux required to generate the exact criterion response
was found by calculating linear regression of the
response values as plotted against a log photon flux
scale. Spectral sensitivity was calculated as 1/photon flux
and values were normalised relative to the maximum
sensitivity for each individual. A mean curve was
produced from 7–9 individual aphids.
Spectral sensitivity was investigated under three
different adaptation conditions: (1) dark adapted,(2)
adapted with white UV-free light,and (3) yellow
adapted (590 nm). Adaptation light was produced by
LEDs and was spectrally characterised with a spectrometer
(TriOs RAMSES ARC) (Fig. 1). The adaptation
light source was fixed to the terminal end of the light
guide. Adaptation time prior to test flashes was 30 min.
The test flashes were delivered under continuous
presence of adaptation light. After pre-adaptation the
duration of the test series for each individual was
40–50 min.
Fig. 1. Normalised irradiance spectrum of LEDs for adaptation
(arbitrary units); UV-free white (continuous line) and yellow (dotted
line).

3. Results
3.1. Form of the electroretinogram
Fig. 2 shows a typical dark adapted ERG recording
elicited from M. persicae. It was found to be biphasic
with a strong corneal negative on-response. The ERG
reading was taken as the voltage difference between the
pre-flash potential and the peak of the negative ERG
component.
3.2. Spectral sensitivity
The spectral sensitivity of the dark adapted compound
eye of M. persicae showed one peak of sensitivity
at 530 nm (Fig. 3). No further peak could be found in
Fig. 2. A typical ERG recording from the green peach aphid at 530 nm
light stimulus as measured by AC amplifier: A ¼ base-line potential,
B ¼ receptor component of ERG,C ¼ off-response,D ¼ duration of
stimulus.
Fig. 3. Spectral sensitivity of the dark-adapted eye of alate M.
persicae. Mean and standard error of 9 individuals (continuous line)
and modelled sensitivity of a green receptor (lmax ¼ 527 nm,dotted
line). For details of modelling see text.
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Fig. 4. Spectral sensitivity of the white-adapted eye of alate M.
persicae. Mean and standard error of 7 individuals.
Fig. 5. Spectral sensitivity of the yellow-adapted eye of alate M.
persicae. Mean and standard error of 7 individuals.
the UV (320–400 nm). In the red region (620–640 nm)
sensitivity was small (o8%). A distinct shoulder was
observed in the sensitivity curve between 500 and
510 nm.
When the eye was tested in the presence of adapting
lights,the spectral sensitivity function showed two
further peaks (Figs. 4 and 5). A UV-sensitive component
with a maximum sensitivity in the region 330–340 nm
appeared when the eye was white- or yellow-adapted. In
addition,in presence of yellow adapting light a blue–
green-sensitive component occurred with a maximum
sensitivity at 490 nm (Fig. 5).
3.3. Fitting a nomogram
The exponential function
a ¼ A exp½ a0x 2 ð1 þ a1xÞŠ

1258
(Stavenga et al.,1993,Eq. (1)),with a the absorbance
at wavelength l, a the sensitivity/100, x¼ 10 logðl=lmaxÞ,
with lmax the wavelength of maximum absorbance,and
A ¼ 1 (as a restriction),was fitted to the long
wavelength tail (580–640 nm) of the sensitivity curves
of the 9 dark adapted aphids by multiple regression
analysis of the linearised form of Eq. (1) with the
statistical programme SAS 6.12 (SAS,1989). The
coefficient of determination was greatest (adjusted
R 2 ¼ 0:971) at lmax ¼ 527 nm,with a0 ¼ 365:31 and
a1 ¼ 4:994. Since the observed dark adapted sensitivity
curve must be seen as the sum of the responses of all
photoreceptors,the model was fitted to the long
wavelength tail of ERG spectral sensitivity. This is
because there,the sensitivity of a potential blue receptor
is negligible in comparison to that of the green receptor.
Therefore,the modelled function can be seen as the
preliminary sensitivity function of the green receptor
(a-band).
4. Discussion
Under the chosen adaptation conditions,the green
peach aphid showed three peaks of spectral sensitivity,
one in the green region around 530 nm,a secondary
blue–green peak (490 nm),and a third in the near UV
(330–340 nm). From this we conclude that M. persicae
possesses three types of photoreceptors.
The existence of a green receptor is evident from the
clear peak at 530 nm in the sensitivity function of the
dark and white adapted animals. With white adapting
light,which reduces the sensitivity of any receptors in
the visible range,the sensitivity function peaks at
330 nm. This indicates the existence of a UV receptor.
Adaptation with 590 nm reduces the sensitivity of the
green receptor more than of any other possible receptors
that have their sensitivity maximum at shorter wavelengths
than 530 nm. So,by yellow adaptation the
maximum sensitivity was shifted from 530 to 490 nm.
This can only be explained by assuming the presence of
a third receptor type sensitive in the blue region.
In addition,at wavelengths below 500 nm,the
modelled green receptor sensitivity clearly differs from
the observed sensitivity function of dark adapted
animals. This is further evidence for the existence of a
blue sensitive photoreceptor in M. persicae (Fig. 3).
From the spectral sensitivity function of the ERG,only
the a-band of the green receptor can be modelled.
Because the b-band cannot be predicted from our
extracellular recordings but also contributes to the
ERG,we could not determine the precise sensitivity
peak of the blue receptor. So,for a validation and a
more precise characterisation of this putative blue
receptor intracellular electrophysiological measurements
are required.
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The evidence for three types of photoreceptors in M.
persicae is surprising as it was assumed earlier from
behavioural observations tests,when spectral sensitivity
data of aphids were not available,‘‘that there are two
receptors in the eye of the aphid,one having a shortwave
peak and the other a yellow peak’’ (Kring,1972,
p. 472). In addition, Gao et al. (2000) found only 2
retinal opsins in the vetch aphid (Megoura viciae
Buckt.),using reverse transcription-PCR of cDNA;
these opsins were classified to be sensitive to UV and
long wavelengths.
Matteson et al. (1992) have concluded from their
research that the phytophagous western flower thrips
(Frankliniella occidentalis) has 1 spectral sensitivity peak
in the ultraviolet and 1 in the visible with a maximum at
around 540 nm. However,the ‘‘double peak’’ they
observed in the visible region of the spectral sensitivity
curve could imply the presence of 2 distinct types of
photoreceptors in this region. In our own ERG
measurements of dark adapted M. persicae,some
individual sensitivity curves also showed a ‘‘double
peak’’. This also suggests the presence of 2 photoreceptor
types with the sensitivity peaks close together,as
found when the animals where yellow adapted.
With M. persicae having 3 types of photoreceptors,it
is remarkable that the ERG of the whitefly (Trialeurodes
vaporariorum) was found to have just 2 spectral peaks in
the ERG (Mellor et al.,1997),since both species share a
number of traits: both are members of the Sternorrhyncha,are
attracted to yellow,and feed on plant sap.
Further investigations are required,using higher wavelength
resolution,adaptation light or intracellular
techniques,in order to specify if the observed differences
between the 2 species are based on their actual
physiology.
Although true colour vision was shown for the
probing behaviour of M. persicae already by Moericke
(1950) (Kelber et al.,2003),wavelength-dependent
behaviour (Goldsmith,1994) may also be involved in
other behaviours of this species. While the experiments
conducted by Moericke (1950) prove colour vision,they
do not allow to infer a specific wavelength of peak
response,as probing was induced in a rather broad
wavelength range of 500–600 nm. Flying black bean
aphids (Aphis fabae Scopoli) were shown to be
maximally responsive to wavelengths in the green region
(530–560 nm) and ultraviolet (360 nm) (Hardie,1989).
Furthermore,the bird cherry aphid (Rhopalosiphum padi
L.) was maximally responsive to targets illuminated
with green (555 nm) and ultraviolet (360 nm) light in a
flight chamber (Nottingham et al.,1991). Wavelengths
4700 nm were not attractive to any of the species. While
these findings suggest that the maximal behavioural
response of aphids more or less coincides with the
maximal reflection of green leaves,at present it is not
possible to speculate how the input from the receptors is

evaluated and translated into behaviour. As the
wavelength discrimination is best where sensitivities of
receptors overlap (Kelber et al.,2003),it might be of
special value to a herbivore to have 2 receptors with
maximal sensitivities laying close together in the blue–
green region. However,in order to back this suggestion,
leaf reflection spectra,as well as further behavioural
experiments and the sensitivities of the single receptors
are needed. This would possibly reveal which role this
combination of photoreceptor types plays in the
evaluation of the physiological state of a plant or in
the visual discrimination of host or non-host plant
species.
Acknowledgements
We would like to thank M. Egelhaaf and R.
Wodjinsky for kindly providing parts of the equipment,
and L. Chittka,J. Spaehte,and T. Spehr for continual
help and stimulating discussions. We especially thank T.
Labhart for valuable suggestions regarding the experimental
set-up and corrections on previous versions of
the manuscript. We are in debt to C. Merx who helped
in the aphid rearing process and Sophie von Lilienfeld-
Toal for their assistance during the experiment. We are
also grateful to R. Heuermann for important comments
concerning the calibration of the ERG apparatus. This
work would not have been possible without benefits
from M.R. Finckh and financial support by the
University of Kassel (ZFF).
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